This invention relates to multi-pole electric machines and, more particularly, to a self-locking block for a field winding in a rotor assembly.
In a conventional electric machine such as a generator having a rotor and a stator, the rotor is provided with field windings that excite the machine while receiving current from an excitation source. The stator is provided with armature windings from which electrical power is provided.
Conventional rotors include axially oriented slots to restrain the winding against centrifugal forces. At the end regions, retaining rings or the like are used to contain the end windings. Due to different radial stiffness of the rotor and retaining ring, bending stresses are generated, and material fatigue becomes a concern. A loose winding may also cause motion of mass, resulting in balance drifts. The issue becomes more significant when lower stiffness composite materials are used for the retaining rings.
It is thus desirable to develop a robust field winding blocking system to control winding position and to reduce its movement on the rotor. Winding blocks can provide adequate pre-stress to keep the winding tight over the design range of spin speeds and provide a well-defined reference position, preventing peripheral dissymmetry in the rotor.
In an exemplary embodiment of the invention, a rotor assembly includes a rotor forging having a rotor body with pole faces, a winding module including a plurality of field windings positioned adjacent the pole faces and winding insulators disposed between each of the field windings, respectively, and a winding block disposed in engagement with the winding module. The winding block is shaped to be shifted to a final position relative to the winding module when the rotor assembly rotates at about its rated speed to thereby compress the winding module.
In another exemplary embodiment of the invention, a multi-pole electric machine rotor assembly includes a rotor forging having a rotor body with poles extending along the direct axis and fins extending along a quadrature axis. Each pole includes a pole face extending generally perpendicularly to the direct axis. A winding module includes a plurality of field windings positioned in spaces between the pole faces and the fins. Winding insulators are disposed between each of the field windings. A winding block is disposed between the winding module and a corresponding one of the fins in each of the spaces between the pole faces and the fins. Preferably, a winding block is movably detached from the fins and the winding module. The winding block may include a support surface engaging a corresponding one of the fins and a tapered surface engaging the winding module. At least one angle of the tapered surface is preferably selected such that the winding block is shifted to a final position when the rotor assembly rotates at about its rated speed. A friction coefficient of the tapered surface may also be selected such that the winding block is shifted to its final position when the rotor assembly rotates at about its rated speed. The winding block is preferably formed of a flexible insulating material.